This invention relates, in general, to semiconductor devices, and more particularly, to a heatsink of a semiconductor package having isolated heatsink bonding pads.
Semiconductor die are housed in semiconductor packages wherein the die is bonded to the flag portion of a heatsink of a leadframe which is then encapsulated in a mold compound. With many die designs, connection means, such as metal wires, are required to electrically connect the semiconductor die to the heatsink. In addition, a connection means may also be required from a lead of the leadframe to the heatsink. The leadframe, including the leads and the heatsink, is comprised of a metal, while the mold compound is comprised of a plastic.
The connection means bonded to the heatsink are subjected to large stresses during temperature cycling, which can occur during testing or field use. The difference in the rate of expansion and contraction of metal and plastic places stress on the connection means and can cause the mold compound to delaminate from the heatsink interface. The delamination of the mold compound creates stress directly on the connection means that often causes the connection means to lift or break. This is highly disadvantageous because semiconductor device failure occurs.
A way of preventing delamination of the mold compound from the heatsink is by altering the chemical composition of the heatsink and/or mold compound to improve adhesion or otherwise minimize the differential in the expansion and contraction of the metal and the plastic of the heatsink and the mold compound. Unfortunately, a reliable metal and plastic system is not known at this time. In addition, because finding a reliable metal and plastic system may be complex, it would be desirable to come up with a simpler, yet effective, solution to the problem.
A method of providing partial isolation of the heatsink and a bonding pad area is known. This method entails forming a hole in the leadframe so that a portion of the heatsink is partially isolated from the rest of the heatsink. It would be desirable to provide for total isolation. In addition, it is very difficult to manufacture holes in the leadframe, and it may be difficult to obtain a flat surface for bonding.
Another problem can arise in the packaging of semiconductor die; when the die is bonded to the heatsink, die attach material such as solder or epoxy may run or splash onto the area of the heatsink where bonding of the connection means is to be made. The die attach material prevents making a reliable bond from the connection means to the heatsink, thus causing device failures in testing or in the field. Because the bonding process is done automatically, and no recognition technique is used, the connection means is bonded to the heatsink in the same area regardless of whether die attach material is present or not. Thus, to ensure that no die attach material has contaminated the heatsink area, the connection means must be bonded to the heatsink further away from the die. This may require either an increase in the size of the package because the heatsink area must be enlarged, or a limit on the size of the die that may be bonded in a certain size package. As is well known, increasing the size of packages is undesirable.
As can be seen, there is a need to prevent these types of connection means bond failures.
Accordingly, it is an object of the present invention to provide a semiconductor package having improved connection means bond reliability.
Another object of the present invention is to provide an improved heatsink of a semiconductor package.
A further object of the present invention is to provide an isolated bonding pad on a heatsink for bonding a connection means.
Yet another object of the present invention is to provide a heatsink having an isolated bonding pad which has a configuration that prevents delamination of a mold compound around a connection means.
Yet a further object of the present invention is to provide a heatsink which prevents die attach material contamination of a connection means to heatsink bond.
Still another object of the present invention is to provide a semiconductor package in which larger die may be housed without increasing the size of the package.